Method of resource block (rb) bundling

ABSTRACT

A method of sizing bundled resource blocks (RBs) having at least one user equipment (UE)-specific demodulation reference signal in an orthogonal frequency division multiplexing (OFDM) system is disclosed. According to one embodiment, the method includes: receiving configuration information related to at least one UE-specific demodulation reference signal; receiving a plurality of resource blocks (RBs) from a network, wherein the plurality of resource blocks comprises the at least one UE-specific demodulation reference signal, at least one cell-specific demodulation reference signal or data, wherein a number of the plurality of RBs is dependent on a size of a system bandwidth, the size of the system bandwidth corresponding to one of four size ranges; and processing at least one of the received plurality of RBs by bundling the plurality of RBs into RB bundles, wherein the size of each RB bundle is based on the one of the four size ranges.

Pursuant to 35 U.S.C. §119(e), this application claims priority to andthe benefit of U.S. Provisional Application Ser. No. 61/259,078, filedon Nov. 6, 2009, the contents of which are incorporated by referenceherein in their entirety.

BACKGROUND

1. Field

Embodiments of the present invention relate to the bundling of resourceblocks (RBs) in a user equipment (UE) performing channel estimationbased on a reference signal.

2. Discussion of the Related Art

The universal mobile telecommunications system (UMTS) is a 3rdGeneration (3G) asynchronous mobile communication system operating inwideband code division multiple access (WCDMA) based on Europeansystems, global system for mobile communications (GSM) and generalpacket radio services (GPRS). The long term evolution (LTE) of UMTS isunder development by the 3rd generation partnership project (3GPP),which standardized UMTS.

In an LTE communication system, a base station may utilize one ofseveral antenna diversity schemes in transmitting data to a mobileterminal (or user equipment (UE)). These antenna diversity schemescorrespond to the number of transmit antennas (or transmit antennaports) used by the base station in transmitting the data to the mobileterminal Transmissions to the mobile terminal include reference signalsused for demodulation of transmitted data.

SUMMARY

Techniques, apparatuses and systems described herein can be used invarious wireless access technologies such as code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), single carrier frequency division multiple access (SC-FDMA),etc. CDMA may be implemented with a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implementedwith a radio technology such as Global System for Mobile communications(GSM), General Packet Radio Service (GPRS), and/or Enhanced Data Ratesfor GSM Evolution (EDGE). OFDMA may be implemented with a radiotechnology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA(E-UTRA), etc. UTRA is a part of a universal mobile telecommunicationsystem (UMTS).

3rd generation partnership project (3GPP) long term evolution (LTE) is apart of an evolved-UMTS (E-UMTS) using the E-UTRA. 3GPP LTE employsOFDMA in downlink and employs SC-FDMA in uplink. LTE-advance (LTE-A) isan evolved version of 3GPP LTE. For purposes of description, particularembodiments are described herein with reference to 3GPP LTE/LTE-A.However, it is understood that embodiments of the present invention maybe implemented in other contexts.

According to one embodiment, a method of sizing bundled resource blocks(RBs) having at least one user equipment (UE)-specific demodulationreference signal in an orthogonal frequency division multiplexing (OFDM)system is disclosed. The method includes: receiving configurationinformation related to at least one UE-specific demodulation referencesignal; receiving a plurality of resource blocks (RBs) from a network,wherein the plurality of resource blocks comprises the at least oneUE-specific demodulation reference signal, at least one cell-specificdemodulation reference signal or data, wherein a number of the pluralityof RBs is dependent on a size of a system bandwidth, the size of thesystem bandwidth corresponding to one of four size ranges; andprocessing at least one of the received plurality of RBs by bundling theplurality of RBs into RB bundles, wherein the size of each RB bundle isbased on the one of the four size ranges.

According to another embodiment, a method of sizing bundled resourceblocks (RBs) having at least one user equipment (UE)-specificdemodulation reference signal in an orthogonal frequency divisionmultiplexing (OFDM) system is disclosed. The method includes:transmitting configuration information related to at least oneUE-specific demodulation reference signal; transmitting a plurality ofresource blocks (RBs) to a user equipment (UE), wherein the plurality ofresource blocks comprises the at least one UE-specific demodulationreference signal, at least one cell-specific demodulation referencesignal or data, wherein a number of the plurality of RBs is dependent ona size of a system bandwidth, the size of the system bandwidthcorresponding to one of four size ranges; and receiving channelcondition information from the UE, wherein the channel conditioninformation is determined by processing at least one of the receivedplurality of RBs by bundling the plurality of RBs into RB bundles,wherein the size of each RB bundle is based on the one of the four sizeranges.

According to another embodiment, a user equipment (UE) sizing bundledresource blocks (RBs) having at least one user equipment (UE)-specificdemodulation reference signal in an orthogonal frequency divisionmultiplexing (OFDM) system is disclosed. The UE includes: an RF unit forreceiving configuration information related to at least one UE-specificdemodulation reference signal and receiving a plurality of resourceblocks (RBs) from a network, wherein the plurality of resource blockscomprises the at least one UE-specific demodulation reference signal, atleast one cell-specific demodulation reference signal or data, wherein anumber of the plurality of RBs is dependent on a size of a systembandwidth, the size of the system bandwidth corresponding to one of foursize ranges; and a processor for processing at least one of the receivedplurality of RBs by bundling the plurality of RBs into RB bundles,wherein the size of each RB bundle is based on the one of the four sizeranges.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present disclosure willbecome more apparent upon consideration of the following description ofembodiments, taken in conjunction with the accompanying drawing figures:

FIG. 1 is a structure of a radio frame of 3GPP LTE.

FIG. 2 illustrates a structure of a resource grid for one downlink slot.

FIG. 3 illustrates a structure of a downlink subframe.

FIG. 4 illustrates a structure of an uplink subframe.

FIG. 5 is a block diagram of a system for implementing embodiments ofthe present invention.

FIG. 6 illustrates a modeling of a MIMO system.

FIG. 7 illustrates a modeling of a MIMO system.

FIG. 8 is a block diagram of a system for implementing SC-FDMA andOFDMA.

FIG. 9 is a block diagram of a system for implementing Uplink SC-FDMA.

FIG. 10 illustrates a structure of an uplink SC-FDMA transmission frame.

FIG. 11 illustrates an example of data signal mapping for a MIMO systembased on SC-FDMA or OFDM.

FIGS. 12A, 12B and 12C illustrate examples of mapping downlink referencesignals.

FIG. 13 illustrates an example of a mapping of a UE-specific RS.

FIG. 14A illustrates an example of channel estimation without RBbundling.

FIG. 14B illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 15A illustrates an example of channel estimation without RBbundling.

FIG. 15B illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 16A illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 16B illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 17A illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 17B illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 18A illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIG. 18B illustrates an example of channel estimation with RB bundlingaccording to one embodiment.

FIGS. 19A, 19B, 19C and 19D illustrate DCI structures according tovarious embodiments.

DETAILED DESCRIPTION

With reference to FIG. 1, a radio frame 10 according to one embodimentincludes 10 subframes. A subframe 101 includes two slots 102 withrespect to the time domain. A time for transmitting one subframe 101 isdefined as a transmission time interval (TTI). For example, one subframe101 may have a length of 1 millisecond (msec), and one slot 102 may havea length of 0.5 msec. One slot 102 includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols with respect to the timedomain (see, e.g., downlink slot 202 of FIG. 2). Since the 3GPP LTE usesthe orthogonal frequency division multiplexing access (OFDMA) in thedownlink, the OFDM symbol is for representing one symbol period. TheOFDM symbol may also be referred to as a single carrier frequencydivision multiple access (SC-FDMA) symbol or a symbol period.

A resource block (RB) is a resource allocation unit, and includes aplurality of contiguous subcarriers in one slot (see, e.g., resourceblock 203 of FIG. 2). As previously noted, FIG. 1 illustrates a radioframe according to one embodiment. It is understood that, according toother embodiments, the number of subframes included in the radio frame,the number of slots included in the subframe, and/or the number of OFDMsymbols included in the slot may vary.

With reference to FIG. 2, a downlink slot 202 is illustrated accordingto one embodiment. The downlink slot 202 includes a plurality of OFDMsymbols with respect to the time domain. The downlink slot 202 includes7 OFDM symbols, and the RB 203 includes 12 subcarriers with respect tothe frequency domain. It is understood that, according to otherembodiments, the size and/or structure of the downlink slot 202 and theRB 203 may vary. Each element on the resource grid is referred to as aresource element (e.g., resource element 204). The RB 203 includes 12×7resource elements 204. The number of RBs (N^(DL)) included in thedownlink slot 202 depends on a downlink transmit bandwidth. Thestructure of an uplink slot may be the same as that of the downlink slot202.

With reference to FIG. 3, a downlink subframe 301 is illustratedaccording to one embodiment. The subframe 301 includes a first slot 302and a second slot 303. With respect to the first slot 302, the firstthree OFDM symbols correspond to a control region 304 to be assigned toa control channel—i.e., a downlink control channel. According to oneembodiment, a maximum of three OFDM symbols located in a front portionof the first slot 302 within the subframe 301 corresponds to a controlregion to be assigned to a control channel. The remaining OFDM symbolscorrespond to a data region 305 to be assigned to a physical downlinkshared channel (PDSCH).

Examples of downlink control channels used in the 3GPP LTE include aphysical control format indicator channel (PCFICH), a physical downlinkcontrol channel (PDCCH), a physical hybrid automatic repeat request(ARQ) indicator channel (PHICH), etc. The PCFICH is transmitted at afirst OFDM symbol of a subframe (e.g., subframe 301 of FIG. 3) andcarries information regarding the number of OFDM symbols used fortransmission of control channels within the subframe. The PHICH is aresponse to an uplink transmission and carries a hybrid automatic repeatrequest (HARQ) acknowledgment (ACK)/non-acknowledgment (NACK) signal.Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI includes uplink or downlinkscheduling information or includes an uplink transmit (Tx) power controlcommand for arbitrary user equipment (UE) groups.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, a resource allocation of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region (e.g., control region 304 of FIG. 3). The UE canmonitor the plurality of PDCCHs.

The PDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups.A format of the PDCCH and the number of bits of the available PDCCH aredetermined according to a correlation between the number of CCEs and thecoding rate provided by the CCEs. The base station (BS) determines aPDCCH format according to a DCI to be transmitted to the UE, andattaches a cyclic redundancy check (CRC) to the control information.

The CRC is masked with a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) according to an owner or usage ofthe PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g.,a cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively,if the PDCCH is for a paging message, a paging indicator identifier(e.g., a paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH isfor system information (e.g., a system information block (SIB), as willbe described in more detail below), a system information identifier anda system information RNTI (SI-RNTI) may be masked to the CRC. Toindicate a random access response that is a response for transmission ofa random access preamble of the UE, a random access-RNTI (RA-RNTI) maybe masked to the CRC.

With reference to FIG. 4, an uplink subframe 40 can be divided withrespect to a frequency domain into a control region 401 and a dataregion 402. The control region 401 is allocated to a physical uplinkcontrol channel (PUCCH) for carrying uplink control information. Thedata region 402 is allocated to a physical uplink shared channel (PUSCH)for carrying user data. To maintain a single carrier property, one UE(i.e., a given UE) does not simultaneously transmit the PUCCH and thePUSCH. The PUCCH for a given UE is allocated an RB pair 403 (i.e., RBs403 a and 403 b) in the subframe 40. The RBs 403 a and 403 b belongingto the RB pair 403 occupy different subcarriers in their respectiveslots (slots 404, 405). In other words, the RB pair allocated to thePUCCH is frequency-hopped in a slot boundary.

With reference to FIG. 5, a wireless communication system includes aNodeB (or Base Station) 51 and one or more UEs 52. To facilitate adownlink, a transmitter may be provided in the NodeB 51, and a receivermay be provided in the UE 52. To facilitate an uplink, a transmitter maybe provided in the UE 52, and a receiver may be provided in the NodeB51.

With continued reference to FIG. 5, the NodeB 51 may include a processor510, a memory 511, and a radio frequency (RF) unit 512. The processor510 may be configured to implement features, procedures and/or methodsdescribed herein with reference to various embodiments. The memory 511is coupled with the processor 510 and stores a variety of informationfor operating the processor 510. The RF unit 512 is coupled with theprocessor 510 and transmits and/or receives a radio signal.

The UE 52 may include a processor 520, a memory 521, and an RF unit 522.The processor 520 may be configured to implement features, proceduresand/or methods described herein with reference to various embodiments.The memory 521 is coupled with the processor 520 and stores a variety ofinformation for operating the processor 520. The RF unit 522 is coupledwith the processor 521 and transmits and/or receives a radio signal.

The NodeB 51 and/or the UE 52 may have a single antenna or multipleantennas. When at least one of the NodeB 10 and the UE 20 has multipleantennas, the wireless communication system may be referred to as amultiple input multiple output (MIMO) system.

A MIMO system uses multiple transmission (Tx) antennas and multiplereception (Rx) antennas to improve the efficiency of Tx/Rx data,relative to a conventional system using a single transmission (Tx)antenna and a single reception (Rx) antenna. In other words, the MIMOtechnology allows a transmission end or a reception end of a wirelesscommunication system to use multiple antennas (hereinafter referred toas “multi-antenna”), so that the capacity or performance can beimproved. For purposes of description, the term “MIMO” will be used torefer to a multi-antenna technology or system.

In more detail, a MIMO system is not dependent on a single antenna pathto receive a single total message. Rather, the MIMO system collects aplurality of data pieces received via several antennas, and completestotal data. As a result, the MIMO technology can increase a datatransfer rate within a specific range, or can increase a system range ata specific data transfer rate.

MIMO technology can be applied to mobile communication technology thatrequires a higher data transfer rate relative to a conventional mobilecommunication technology. MIMO communication technology can be appliedto mobile communication terminals or repeaters, for example, to extend adata communication range. As such, it can address the limited amount oftransfer data often provided by other mobile communication systems.

Among a variety of technologies capable of improving the transferefficiency of data, MIMO technology can greatly increase an amount ofcommunication capacity and Tx/Rx performances without allocatingadditional frequencies or requiring additional power.

With reference to FIG. 6, a block diagram of a MIMO system isillustrated. The transmitter 61 has a number of transmission (Tx)antennas. The receiver 62 has a number of reception (Rx) antennas. Ifthe number of transmission (Tx) antennas is increased to N_(T) and thenumber of reception (Rx) antennas is increased to N_(R), a theoreticalchannel transmission capacity of the MIMO communication system increasesin proportion to the number of antennas. Relative to a previouslyexisting system in which only a transmitter or only a receiver usesseveral antennas, a transfer rate and a frequency efficiency of a MIMOsystem (such as the system illustrated in FIG. 6) may be greatlyincreased.

Regarding such a MIMO system, the transfer rate obtained by theincreasing channel transmission capacity is equal to the multiplicationof a rate increment (R_(i)) and a maximum transfer rate (R_(o)) that isobtained when a single antenna is used. The rate increment (R_(i)) canbe expressed according to Equation 1 below.

R_(i)=min(N_(T),N_(R))   [Equation 1]

A mathematical modeling of a usage of the above-mentioned MIMO systemwill now be described in more detail. As explained with reference toFIG. 6, the system has N_(T) Tx antennas and N_(R) Rx antennas. In thecase of a transmission (Tx) signal, a maximum number of pieces oftransmission information is N_(T) under the condition that N_(T) Txantennas are used, so that the Tx signal can be represented as a vectoras shown in Equation 2 below.

s=[s₁, s₂, . . . , s_(N) _(T) ]^(T)   [Equation 2]

Individual transmission information pieces (s₁, s₂, . . . , s_(NT)) mayhave different transmission powers relative to one another. In thiscase, if the individual transmission powers are denoted by (P₁, P₂, . .. , P_(NT)), transmission information having an adjusted transmissionpower can be represented as a vector as shown in Equation 3 below.

ŝ=[ŝ₁, ŝ₂, . . . , ŝ_(N) _(T) ]^(T)=[P₁s₁, P₂s₂, . . . , P_(N) _(T)s_(N) _(T) ]^(T)   [Equation 3]

In Equation 3, ŝ is a diagonal matrix of a transmission power, and canbe represented by Equation 4 below.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The information vector ŝ having an adjusted transmission power ismultiplied by a weight matrix (W), so that N_(T) transmission (Tx)signals (x₁, x₂, . . . , x_(NT)) to be transmitted are configured. Inthis case, the weight matrix (or precoding matrix) is adapted toproperly distribute Tx information to individual antennas according toTx-channel situations. The above-mentioned Tx signals (x₁, x₂, . . . ,x_(NT)) can be represented by Equation 5 below using the vector (x).

$\begin{matrix}\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}}} \\{{{= \quad}W\hat{s}} = {WPs}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, w_(ij) is a weight between the i-th Tx antenna and thej-th Tx information, and W is a matrix indicating the weights wij. Thematrix W is referred to as a weight matrix or a precoding matrix. Theabove-mentioned Tx signal (x) can be considered in different waysaccording to two configurations, i.e., a first configuration in whichspatial diversity is used and a second configuration in which spatialmultiplexing is used. When spatial multiplexing is used, differentsignals are multiplexed together, and the multiplexed signals aretransmitted to a destination, so that elements of the information vector(s) have different values. When spatial diversity is used, the samesignal is repeatedly transmitted via several channel paths, so thatelements of the information vector (s) have the same value.

It is understood that a combination of the spatial multiplexing schemeand the spatial diversity scheme may also be considered. For example,the same signal may be transmitted via three Tx antennas according tothe spatial diversity scheme, and the remaining signals are spatiallymultiplexed and then transmitted to a destination.

Regarding the receiver end, if N_(R) Rx antennas are used in the MIMOsystem of FIG. 6, Rx signals (y₁, y₂, . . . , y_(NR)) of the individualantennas can be represented as a specific vector (y) as shown inEquation 6 below.

y=[y₁, y₂, . . . , y_(N) _(R) ]^(T)   [Equation 6]

In modeling channels of the MIMO communication system, individualchannels can be distinguished from each other according to Tx/Rx antennaindexes. A specific channel passing from a Tx antenna (j) to an Rxantenna (i) is denoted as h_(ij). Multiple channels that are associatedwith each other (see, e.g., FIG. 7) may be represented in the form of avector or matrix.

With reference to FIG. 7, N_(T) channels are shown, each of the channelspassing from a respective Tx antenna to an Rx antenna (i). The channelspassing from the respective Tx antennas to the Rx antenna (i) can berepresented using Equation 7 below.

h_(i) ^(T)=[h_(i1), h_(i2), . . . , h_(iN) _(T) ]  [Equation 7]

If all channels passing from the N_(T) Tx antennas to the N_(R) Rxantennas are denoted using the matrix shown in Equation 7, then thechannel matrix of Equation 8 below may be obtained.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In modeling the channels, an Additive White Gaussian Noise (AWGN) may beadded to a signal which passes through the channel matrix H shown inEquation 8. The AWGN (n₁, n₂, . . . , n_(NR)) added to the signalsreceived at each of the N_(R) Rx antennas can be represented as aspecific vector as shown in Equation 9 below.

n=[n₁, n₂, . . . , n_(N) _(R) ]^(T)   [Equation 9]

According to the above-described modeling method of the Tx signal, theRx signal, and the AWGN, the MIMO communication system can berepresented by Equation 10 below.

$\begin{matrix}\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}}}} \\{= {{Hx} + n}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The number of rows and the number of columns of a channel matrix Hindicating a channel condition is determined by the number of Tx/Rxantennas. In the channel matrix H, the number of rows is equal to thenumber (N_(R)) of Rx antennas, and the number of columns is equal to thenumber (N_(T)) of Tx antennas. As such, the channel matrix H is anN_(R)×N_(T) matrix.

Generally, a matrix rank is defined by the smaller of the number of rowsand the number of columns, where the rows and the columns areindependent of each other. Therefore, the matrix rank cannot be higherthan the number of rows or columns The rank of the channel matrix H canbe represented by Equation 11 below.

rank(H)≦min(N_(T), N_(R))   [Equation 11]

Now, the precoding matrix will be described in more detail. First, aspreviously described, the channel matrix H (i.e., the matrix withouttaking into account the precoding matrix) can be represented as shown inEquation 12 below.

$\begin{matrix}\begin{matrix}{H = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}} \\{= \begin{bmatrix}h_{1} & h_{2} & \ldots & h_{N_{T}}\end{bmatrix}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In general, a k-th received SINR (Signal to Interference Noise Ratio)ρ_(k) is defined according to Equation 13 below if the receiver uses aminimum mean square error (MMSE) estimator, i.e., if the receiver is anMMSE receiver.

$\begin{matrix}{\rho_{k} = {{SINR}_{k} = {{h_{k}^{H}\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{h_{i}h_{i}^{H}}}} \right)}^{- 1}h_{k}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

The effective channel matrix {tilde over (H)} which takes into accountthe precoding matrix W can be represented according to Equation 14below.

$\begin{matrix}\begin{matrix}{\overset{\sim}{H} = {{HW} = {\begin{bmatrix}{\overset{\rightarrow}{h}}_{1}^{T} \\{\overset{\rightarrow}{h}}_{1}^{T} \\\vdots \\{\overset{\rightarrow}{h}}_{N_{R}}^{T}\end{bmatrix}\begin{bmatrix}w_{1} & w_{2} & \ldots & w_{N_{R}}\end{bmatrix}}}} \\{= \begin{bmatrix}{{\overset{\rightarrow}{h}}_{1}^{T}w_{1}} & {{\overset{\rightarrow}{h}}_{1}^{T}w_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{N_{R}}} \\{{\overset{\rightarrow}{h}}_{2}^{T}w_{1}} & {{\overset{\rightarrow}{h}}_{2}^{T}w_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{N_{R}}} \\\vdots & \vdots & \vdots & \vdots \\{{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{1}} & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{N_{R}}}\end{bmatrix}} \\{= \begin{bmatrix}{\overset{\sim}{h}}_{1} & {\overset{\sim}{h}}_{2} & \ldots & {\overset{\sim}{h}}_{N_{T}}\end{bmatrix}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Therefore, the k-th effective received SINR {tilde over (ρ)}_(k) isdefined according to Equation 15 below if it is assumed that the MMSEreceiver is used.

$\begin{matrix}{{\overset{\sim}{\rho}}_{k} = {{SINR}_{k} = {{{{\overset{\sim}{h}}_{k}^{H}\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{{\overset{\sim}{h}}_{i}{\overset{\sim}{h}}_{i}^{H}}}} \right)}^{- 1}{\overset{\sim}{h}}_{k}} = {\quad{\begin{bmatrix}{w_{k}^{H}{\overset{\rightarrow}{h}}_{1}^{*}} & {w_{k}^{H}{\overset{\rightarrow}{h}}_{2}^{*}} & \ldots & {w_{k}^{H}{\overset{\rightarrow}{h}}_{N_{R}}^{*}}\end{bmatrix}{\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{{\overset{\sim}{h}}_{i}{\overset{\sim}{h}}_{i}^{H}}}} \right)^{- 1}\begin{bmatrix}{{\overset{\rightarrow}{h}}_{1}^{T}w_{k}} \\{{\overset{\rightarrow}{h}}_{2}^{T}w_{k}} \\\vdots \\{{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{k}}\end{bmatrix}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

Here, based on theoretical notions, we can observe some effectiveness onthe received SINR depending on variations of the precoding matrix.First, we can check on an effectiveness of permutating columns in oneprecoding matrix. Via a permutation between the i-th column vector w_(i)and the j-th column vector w_(j), a permutated precoding matrix Ŵ can berepresented according to Equation 16 below.

W=└w₁ . . . w_(i) . . . w_(j) . . . w_(N) _(R) ┘

Ŵ=[w₁ . . . w_(j) . . . w_(i) . . . w_(N) _(R) ]  [Equation 16]

The effective channel {tilde over (H)} with precoding matrix W and thepermutated effective channel Ĥ with precoding matrix Ŵ can berepresented according to Equation 17 below.

$\begin{matrix}\begin{matrix}{\overset{\sim}{H} = {{HW} = {\begin{bmatrix}{\overset{\rightarrow}{h}}_{1}^{T} \\{\overset{\rightarrow}{h}}_{1}^{T} \\\vdots \\{\overset{\rightarrow}{h}}_{N_{R}}^{T}\end{bmatrix}\begin{bmatrix}w_{1} & \ldots & w_{i} & \ldots & w_{j} & \ldots & w_{N_{R}}\end{bmatrix}}}} \\{= {\quad\begin{bmatrix}{{\overset{\rightarrow}{h}}_{1}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{N_{T}}} \\{{\overset{\rightarrow}{h}}_{2}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{N_{T}}} \\\vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\{{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{N_{T}}}\end{bmatrix}}} \\{= {\quad\begin{bmatrix}{\overset{\sim}{h}}_{1} & \ldots & {\overset{\sim}{h}}_{i} & \ldots & {\overset{\sim}{h}}_{j} & \ldots & {\overset{\sim}{h}}_{N_{T}}\end{bmatrix}}} \\{\hat{H} = {{H\hat{W}} = {\begin{bmatrix}{\overset{\rightarrow}{h}}_{1}^{T} \\{\overset{\rightarrow}{h}}_{1}^{T} \\\vdots \\{\overset{\rightarrow}{h}}_{N_{R}}^{T}\end{bmatrix}\begin{bmatrix}w_{1} & \ldots & w_{j} & \ldots & w_{i} & \ldots & w_{N_{R}}\end{bmatrix}}}} \\{= \left\lbrack \begin{matrix}{{\overset{\rightarrow}{h}}_{1}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}w_{N_{T}}} \\{{\overset{\rightarrow}{h}}_{2}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}w_{N_{T}}} \\\vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots \\{{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{1}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{j}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{i}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}w_{N_{T}}}\end{matrix} \right\rbrack} \\{= \begin{bmatrix}{\overset{\sim}{h}}_{1} & \ldots & {\overset{\sim}{h}}_{j} & \ldots & {\overset{\sim}{h}}_{i} & \ldots & {\overset{\sim}{h}}_{N_{T}}\end{bmatrix}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

Based on Equation 17, even if two column vectors are permutated, thereceived SINR value itself is not changed (except as to order) such thatthe channel capacity/sum rate is constant. Similar to Equations 14 and15, the permutated effective channel and the k-th received SINR{circumflex over (ρ)}_(k) can be respectively determined according toEquations 18 and 19 below.

$\begin{matrix}\begin{matrix}{\hat{H} = {{H\hat{W}} = {\begin{bmatrix}{\overset{\rightarrow}{h}}_{1}^{T} \\{\overset{\rightarrow}{h}}_{1}^{T} \\\vdots \\{\overset{\rightarrow}{h}}_{N_{R}}^{T}\end{bmatrix}\begin{bmatrix}{\hat{w}}_{1} & {\hat{w}}_{2} & \ldots & {\hat{w}}_{N_{R}}\end{bmatrix}}}} \\{= {\quad\begin{bmatrix}{{\overset{\rightarrow}{h}}_{1}^{T}{\hat{w}}_{1}} & {{\overset{\rightarrow}{h}}_{1}^{T}{\hat{w}}_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{1}^{T}{\hat{w}}_{N_{R}}} \\{{\overset{\rightarrow}{h}}_{2}^{T}{\hat{w}}_{1}} & {{\overset{\rightarrow}{h}}_{2}^{T}{\hat{w}}_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{2}^{T}{\hat{w}}_{N_{R}}} \\\vdots & \vdots & \vdots & \vdots \\{{\overset{\rightarrow}{h}}_{N_{R}}^{T}{\hat{w}}_{1}} & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}{\hat{w}}_{2}} & \ldots & {{\overset{\rightarrow}{h}}_{N_{R}}^{T}{\hat{w}}_{N_{R}}}\end{bmatrix}}} \\{= {\quad\left\lfloor \begin{matrix}{\hat{h}}_{1} & {\hat{h}}_{2} & \ldots & {\hat{h}}_{N_{T}}\end{matrix} \right\rfloor}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack \\{{\hat{\rho}}_{k} = {{SINR}_{k} = {{{\hat{h}}_{k}^{H}\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{{\hat{h}}_{i}{\hat{h}}_{i}^{H}}}} \right)}^{- 1}{\hat{h}}_{k}}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

Based on Equation 19, the interference and noise parts (orcontributions) can be expressed according to Equation 20 below.

$\begin{matrix}{\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{{\hat{h}}_{i}{\hat{h}}_{i}^{H}}}} \right)^{- 1} = \begin{bmatrix}a_{11}^{k} & a_{12}^{k} & \ldots & a_{1N_{R}}^{k} \\a_{21}^{k} & a_{22}^{k} & \ldots & a_{2N_{R}}^{k} \\\vdots & \vdots & \vdots & \vdots \\a_{N_{R}1}^{k} & a_{N_{R}2}^{k} & \ldots & a_{N_{R}N_{R}}^{k}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

The newly received SINR {circumflex over (ρ)}_(k) can be representedaccording to Equation 21 below.

$\begin{matrix}\begin{matrix}{{\hat{\rho}}_{k} = {{SINR}_{k} = {{{\hat{h}}_{k}^{H}\left( {{N_{0}I_{N_{R}}} + {\sum\limits_{\underset{i \neq k}{i = 1}}^{N_{R}}{{\hat{h}}_{i}{\hat{h}}_{i}^{H}}}} \right)}^{- 1}{\hat{h}}_{k}}}} \\{= {{{\hat{h}}_{k}^{H}\begin{bmatrix}a_{11}^{k} & a_{12}^{k} & \ldots & a_{1N_{R}}^{k} \\a_{21}^{k} & a_{22}^{k} & \ldots & a_{2N_{R}}^{k} \\\vdots & \vdots & \vdots & \vdots \\a_{N_{R}1}^{k} & a_{N_{R}2}^{k} & \ldots & a_{N_{R}N_{R}}^{k}\end{bmatrix}}{\hat{h}}_{k}}} \\{= {\sum\limits_{i = 1}^{N_{R}}{\sum\limits_{j = 1}^{N_{R}}{{\hat{w}}_{k}{\overset{\rightarrow}{h}}_{i}^{*} \times a_{ij} \times {\overset{\rightarrow}{h}}_{j}^{T}{\hat{w}}_{k}}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 21} \right\rbrack\end{matrix}$

Also, we can check on the effectiveness of multiplexing e^(−jθ)(0≦θ≦2π)to a specific column vector in one precoding matrix. Simply ±1,±j can bepossible values, for example. {tilde over (W)}_(k) where e^(−jθ) ismultiplexed to the k-th column of the permutated precoding matrix Ŵ canbe represented according to Equation 22 below.

{tilde over (W)} _(k) =e ^(−jθ) Ŵ _(k)   [Equation 22]

Here, the received SINR {tilde over (ρ)}_(k) can be representedaccording to Equation 23 below.

$\begin{matrix}\begin{matrix}{{\overset{\sim}{\rho}}_{k} = {\sum\limits_{i = 1}^{N_{R}}{\sum\limits_{j = 1}^{N_{R}}{{\overset{\sim}{w}}_{k}{\overset{\rightarrow}{h}}_{i}^{*} \times a_{ij} \times {\overset{\rightarrow}{h}}_{j}^{T}{\hat{w}}_{k}}}}} \\{= {\sum\limits_{i = 1}^{N_{R}}{\sum\limits_{j = 1}^{N_{R}}{^{+ {j\theta}}{\hat{w}}_{k}{\overset{\rightarrow}{h}}_{i}^{*} \times a_{ij} \times {\overset{\rightarrow}{h}}_{j}^{T}^{- {j\theta}}{\hat{w}}_{k}}}}} \\{= {\sum\limits_{i = 1}^{N_{R}}{\sum\limits_{j = 1}^{N_{R}}{{\hat{w}}_{k}{\overset{\rightarrow}{h}}_{i}^{*} \times a_{ij} \times {\overset{\rightarrow}{h}}_{j}^{T}{\hat{w}}_{k}}}}} \\{= {\hat{\rho}}_{k}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 23} \right\rbrack\end{matrix}$

According to Equation 23, multiplexing e^(−jθ) to a specific columnvector in the precoding matrix does not affect the received SINR andchannel capacity/sum rate.

In general, in a multi-Input multi-output (MIMO) antenna system based onOFDM (Orthogonal Frequency Division Multiplexing) or SC-FDMA (SingleCarrier-Frequency Division Multiple Access), the data signal goesthrough complex mapping relations within a transmission symbol. First,the data to be transmitted are separated into codewords. For mostapplications, the codeword will be equivalent to a transport block givenby the MAC (Medium Access Control) layer. Each codeword is encodedseparately using a channel code such as Turbo Code or Tail bitingconvolutional code. After encoding and rate matching to appropriatesizes, the codeword is then mapped to ‘layers’. Referring to FIG. 8, foran SC-FDMA transmission DFT (Discrete Fourier Transform), precoding isperformed for each layer (see, for example, DFT 801), and, for OFDMtransmission, no DFT transform is applied. Then, the DFT transformedsignal in each layer is multiplied by the precoding vector/matrix andmapped to transmission antenna ports. Note that the transmission antennaports can be once again mapped to actual physical antennas by means ofantenna virtualization.

In general, the cubic metric (CM) of a single carrier signal (such asSC-FDMA transmission signals) is much lower than that of multi carriersignals. This general concept also applies to peak power to averagepower ratios (PAPR). Both CM and PAPR are related to the dynamic rangewhich the power amplifier (PA) of the transmitter must support. Underthe same PA, any transmission signal which has a lower CM or PAPR thansome other form of signal can be transmitted at a higher transmit power.Conversely, if the PA's maximum power is fixed and the transmitter wantsto send a high CM or PAPR signal, then it must reduce the transmit powerslightly more than the situation involving a low CM signal. The reasonwhy a single carrier signal has a lower CM than multi-carrier signals isthat, in multi-carrier signals, multiple signals overlap and sometimesresult in co-phase addition of signals. This possibility can lead to alarge signal amplitude. This is why an OFDM system has large PAPR or CMvalues.

If a resulting signal y only consists of information symbol x1, thenthis signal can be considered as a single carrier signal (e.g., y=x1).But, if the resulting signal y consists of multiple information symbolsx1, x2, x3, . . . , xN, then the signal can be considered as amulti-carrier signal such as y=x1+x2+x3+ . . . +xN. The PAPR or CM isproportional to the number of information symbols coherently addedtogether in the resulting signal waveform, but the values tend tosaturate after a certain number of information symbols are addedtogether. So, if the resulting signal waveform is created by theaddition of relatively few single carrier signals, then the CM or PAPRwould be much lower than multi-carrier signals but slightly higher thana pure single carrier signal.

In Rel-8 LTE, a system structure and a transmission frame for the uplinkSC-FDMA are shown in FIG. 9 and FIG. 10, respectively. With reference toFIG. 10, the basic transmission unit is a subframe 1000. Two slots 1010,1020 make up subframe 1000, and, depending on a Cyclic Prefix (CP)configuration (e.g. Normal CP or Extended CP), the number of SC-FDMAsymbols in a slot is 7 or 6. In each slot 1010, 1020, there is at least1 reference signal SC-FDMA symbol 1030, 1040, which is not used for datatransmission. Within a single SC-FDMA symbol, there are multiplesubcarriers. A Resource Element (RE) is a complex information symbolmapped to a single subcarrier. If DFT transform precoding is used, theRE is the single information symbol mapped to a DFT transform indexsince DFT transform size and the number of subcarriers used intransmission is the same for SC-FDMA.

In an LTE-advanced system, spatial multiplexing of up to four layers isconsidered for the uplink transmission. In the uplink using single userspatial multiplexing, up to two transport blocks can be transmitted froma scheduled terminal in a subframe per uplink component carrier.Depending on the number of transmission layers, the modulation symbolsassociated with each of the transport blocks are mapped onto one or twolayers according to the same principle as Rel-8 LTE downlink spatialmultiplexing. Moreover, DFT-precoded OFDM is adopted as the multipleaccess scheme for uplink data transmission both in absence and presenceof spatial multiplexing. In the case of multiple component carriers,there is one DFT per component carrier. In LTE-advanced, in particular,both frequency-contiguous and frequency-non-contiguous resourceallocation are supported on each component carrier.

FIG. 11 depicts an example of data signal mapping relation for a MIMOsystem based on the SC-FDMA transmission. If the number of codewords isNC, and the number of layers is NL, NC number of information symbols ormultiples of NC number of information symbols will be mapped to NLnumber of symbols or multiples of NL (see, for example, mapping 1100).DFT transform precoding for SC-FDMA does not change the size of thelayer. When precoding is performed to layers, the number of informationsymbols will change from NL to NT, by the NT by NL matrixmultiplication. Generally the transmission ‘rank’ of the spatiallymultiplexed data is equal to the number of layers conveying data in agiven transmission instant (NL, for example).

LTE (Long Term Evolution) and LTEA (Long Term Evolution Advanced)

In general, LTE (Long Term Evolution) refers to the evolved version ofUMTS, or E-UMTS in the 3GPP (3rd Generation Partnership Project). Thedevelopment of UMTS specifications in 3GPP is classified by its releasenumber. For example, Release 99 indicates the WCDMA (Wideband CodeDivision Multiple Access) standard which consists of specifications withthe number starting with TS (Technical Specification) 25.XXX. As theWCDMA specification grows, its release number also increases to Release4 and Release 5 and so on. LTE may be considered as a quantum jump fromWCDMA: some features may not be backward compatible with WCDMA.Accordingly, the specification number of LTE starts with TS 36.XXX andnot TS 25.XXX. In addition, LTE has its own release number—i.e., 8.Since LTE will likely evolve as time progresses, its release number willincrease from 8 to a larger number. Due to the increased demand forenhanced features, an upgraded version of LTE was introduced, e.g.,release number 10 or higher, which is also referred to as LTEA (LongTerm Evolution Advanced).

Hereinafter, LTE refers to the standards of release 8 or 9 in 3GPPE-UMTS, and LTEA refers to the standards of release 10 or later in 3GPPE-UMTS.

Since the development of LTE can be categorized according to its releasenumber, it is also possible to refer to LTEA as LTE release 10.Therefore, the term LTE release XX will be used to indicate a specificset of standards. To be more specific, LTE release 8 or later will beused to refer to all standards including LTE and LTEA. LTE release 10 orlater will be used to refer to LTEA. For convenience of notation, if astrict discrimination between LTE and LTEA is not necessarily required,the term LTE can be generally used to refer to all standards startingfrom LTE release 8 through LTE release 10 or a later release.

RB (Resource Block)

In LTE, OFDM (Orthogonal Frequency Division Multiplexing) is adopted asan air interface technology. OFDM chops the frequency bandwidth intomultiple subbands which are orthogonal to each other, i.e., subcarriers.These subcarriers are used as pipes and are distributed to several UEsto transmit data. Since OFDM provides another dimension of multiplexingUE data (i.e., in the frequency domain while a conventionalcommunication system enables multiplexing of UE data in the time domain)a two-dimensional unit is utilized to model the resource in OFDM. Forthis purpose, according to one embodiment, the resource block (RB) isdefined as a two-dimensional unit in both the time and the frequencydomain in LTE. The RB may be considered as a minimal two-dimensionalunit in the time and frequency domains. The RB spans 180 kHz in thefrequency domain and 0.5 milliseconds in the time domain. In moredetail, a single RB corresponds to 12 subcarriers and either 7 or 6 OFDMsymbols. The number of OFDM symbols in one RB depends on the framestructure based on CP length.

RS (Reference Signal)

Communications on a wireless channel inherently experience considerablenoise and interference in the transmission of data, which results indifficulties on the receiver side. To correct for errors caused by thechannel, it is required for the receiver to know the channelvariation(s) exactly and instantaneously (or almost instantaneously). Inorder to allow the receiver to determine the channel variation rathereasily, a predetermined signal which is known at both the transmitterand the receiver sides may be employed. The insertion of a known signalin the transmission resource facilitates channel estimation at thereceiver. However, because it occupies some portion of the resource,inserting the known signal also sacrifices, at least to some degree, thecapacity of system transmission.

The predetermined known signal for channel estimation is referred to asthe pilot signal, reference signal or training signal. The moreinformation the RS carries, the more exact the channel estimation.However, increasing the information carried by the RS also brings aboutadded sacrifice of system throughput. Therefore, the size and locationof the RS should be carefully considered in view of the tradeoff betweenchannel estimation performance and system throughput loss.

Resources in LTE have two dimensions in time and frequency domain; theRS also is located along two dimensions. In order to guarantee theminimum channel estimation performance in two dimensions, the RS isdesigned to be spread out along the time and frequency domain in asomewhat uniformed manner. A placement of the RS in LTE for asingle-antenna configuration, a two-antenna configuration and afour-antenna configured is illustrated with reference to FIGS. 12A, 12Band 12C, respectively, with respect to various embodiments. Theplacement of the RS is described in more detail in co-appending U.S.application Ser. No. 12/788,750, the disclosure of which is incorporatedherein by reference in its entirety.

Recently, in order to support the demanding increase of throughput, MIMOtechnology has been intensively studied and also adopted in LTE. MIMOtechniques introduce an additional dimension as a resource, which isreferred to as layer, rank, or virtual antenna, for example. Theadditional dimension gives rise to the problem of including the RS in aMIMO transmission. Here, the RS should be carefully designed to balancethe performance between spatial domains. With reference to FIGS. 12A,12B and 12C, it is illustrated that the RS for each layer is spread outin a balanced manner (see, e.g., FIG. 12B, in which the RS for atwo-antenna configuration is illustrated, and FIG. 12C, in which the RSfor a four-antenna configuration is illustrated).

UE-Specific Demodulation Reference Signal

In LTE Release 8, the RS in the downlink is generated in a cell-specificmanner. That is, all the UEs in a given cell should use the same RS.Using the same RS for all UEs may be quite reasonable when demodulatinga common signal such as the common control signal. However, when usingthe RS for data demodulation, the situation could be quite different.This is because the data may be targeted for only a particular UE (e.g.,one or more targeted or specific UEs) and not for all UEs in a givencell. Therefore, according to one embodiment, the RS in a data downlinkis generated and transmitted for only a targeted UE. An RS configuredfor only a targeted (or scheduled) UE is referred to as a UE-specific RSor a UE-dedicated RS.

In LTE release 9 or later, a MIMO scheme is extended to supportdual-layer beamforming or 8 transmission antennas so that additional RSis to be incorporated into the data by utilizing some resources in LTErelease 8 but minimizing the impact on LTE release 8. In order to reduceor minimize the impact on the performance of LTE release 8, the amountof additional overhead for UE-specific demodulation RS should becarefully considered. The amount of the UE-specific RS cannot be reducedsignificantly because reducing the RS too significantly may unacceptablyreduce the performance of channel estimation for data demodulation inthe scheduled UE. Therefore the trade-off between the channel estimationperformance for demodulation and the adverse impact on LTE release 8legacy UEs should be carefully considered.

With reference to FIG. 13, one example of the mapping of UE-specific RSin one RB is illustrated. As illustrated in FIG. 13, certain resources(e.g., resource elements 1300) are reserved for UEs of a given cell, andother resources (e.g., resource elements 1310) are reserved for one ormore specific UEs in the given cell.

Bundling of Resource Blocks in UE-Specific Demodulation RS

In order to achieve adequate channel estimation accuracy by using arelatively small amount of UE-specific RS, RBs in UE-specificdemodulation RS may be bundled. Under this approach, a UE can estimate achannel based on the RSs from a bundling of several contiguous RBs andnot from only a single RB. The RB bundling of the RS expands the span ofsampled RSs in the frequency and time domains, which provides the UEwith the freedom to perform additional processing in channel estimation,which, in turn, results in better channel estimation performance. Sincethe bundling of continuous RBs in UE-specific demodulation RS increasesthe performance of channel estimation, the actual amount of RS in one RBcan be reduced with the required channel estimation capability stillmet. Examples of channel estimation based on RS without and withbundling of RBs are illustrated in FIGS. 14A and 14B, respectively.

With reference to FIG. 14A, a UE estimates the channel based on the RSsof individual RBs. That is, the UE estimates the channel based on RB1410 in isolation, on RB 1420 in isolation, and on RB 1430 in isolation.It is understood that, although the channel estimation is performedbased on each RB in isolation, this approach does not necessarilyrequire the implementation of multiple channel estimators. Rather, thechannel estimation per each RB may be performed sequentially by a singlechannel estimator in a timely manner.

With reference to FIG. 14B, the UE estimates the channel based on theRSs of a bundle of two or more RBs. That is, the UE estimates thechannel based on a bundle of RBs including RBs 1410, 1420, 1430concurrently (the UE concurrently uses or processes a combination of theRS information provided in the RBs 1410, 1420 and 1430). A maindifference between FIG. 14A and FIG. 14B is the dimension of the channelestimator. Since the channel estimator in FIG. 14B has, at a given time,access to a higher quantity of RS than the channel estimator in FIG.14A, the former has additional freedom of signal processing on thechannel estimation.

Resource Block Allocation

OFDM gives the freedom to allocate subcarriers to each scheduled user upto a FFT (Fast Fourier Transform) size. In LTE, more than 1000subcarriers can be used depending on the bandwidth. However, thesubcarrier is not the unit of actual usage in the resource allocation.Instead, a set of subcarriers is defined to alleviate the overhead ofcontrol signaling in the resource allocation. The set of subcarriers isthe earlier-described RB. The introduction of the RB significantlydecreases the amount of control signaling in the allocation; e.g., inthe bandwidth spanning 20 MHz, where approximately 100 RBs span 1200subcarriers, 1200 indications are needed for individual subcarriersallocated to individual users, while only 100 indications are requiredwhere individual RBs are allocated to individual users. 100 indicationsin 20 MHz may be viewed as an undesirably high amount of overhead insome cases. In such situations, a higher level of reduction in thenumber of indications would be needed. For this purpose, the allocationof RB to scheduled UEs could be restricted to a contiguous group of RBs.

One example of allocating groupings of RBs is illustrated in Table 1below.

TABLE 1 System Bandwidth RB grouping Size ≦10 1 11-26 2 27-63 3  64-1104

According to Table 1, in allocating downlink resources to UEs, a groupof a certain number of contiguous RBs is allocated to a UE. The numberof RBs varies depending on the system bandwidth. For example, accordingto Table 1, when the system bandwidth is 10 RBs or less, then a group of1 RB is allocated to the user. Also, when the system bandwidth is 11 to26 RBs, then a group of 2 contiguous RBs is allocated to the user. Whenthe system bandwidth is 27 to 63 RBs, then a group of 3 contiguous RBsis allocated to the user. When the system bandwidth is 64 to 110 RBs,then a group of 4 contiguous RBs is allocated to the user.

The minimum unit of downlink resource allocation could be restricted toa multiple of the sizes listed in Table 1 according to the systembandwidth.

Granularity of CQI Reporting

The downlink channel status of a UE may be used to decide which UEshould be scheduled (i.e., which UE is assigned downlink resources). Inorder to optimize the utilization of resources, the UE having the bestchannel condition in a given frequency should be allocated. Even in afair scheduler, the channel quality indication is still vitalinformation used in operating the scheduler. In TDD (Time DivisionDuplex), channel symmetry between uplink and downlink may be used toalleviate the burden of reporting channel status from a UE to a basestation (e.g., a NodeB).

That is not the case for FDD (Frequency Division Duplex) since theuplink channel status which may be measured by the NodeB is quitedifferent from the downlink channel status which is measured by the UE.Therefore, a channel status reporting scheme is implemented in LTE, andthe indicator is referred to as a CQI (Channel Quality Indicator). TheCQI provides key information to the NodeB for improved scheduling ofdownlink resources to the UEs.

CQI is a measurement of a channel status, a degree to which a channelcan transmit data with an error rate lower than a predetermined errorrate. In a conventional (e.g., non-MIMO) system, the CQI can berepresented as a single measurement, i.e., SNR (Signal-to-Noise Ratio),SINR (Signal-to-Interference-and-Noise Ratio), or MCS (Modulation andCoding Scheme) Index. However, in a system using MIMO, CQI should alsocover the expanded dimension, i.e., the space domain. The use ofmultiple antennas adds freedom in space, which may be measured in theform of an RI (Rank Index). Moreover, a more sophisticated MIMO schemecould be used, e.g., a Precoded MIMO system, in SM (SpatialMultiplexing) or Beamforming, which requires another indication ofprecoding, e.g., PMI (Precoding Matrix Indication). According to oneembodiment, the CQI in a MIMO system may include the MCS, RI and PMI.

CQI could be interpreted as that it has a meaning only when it isrelated to the downlink assignment. However, downlink channel assignmentcould be done by the expanded size of RBs as explained in the previoussection, which requires the corresponding CQI reporting to match thesize of unit for downlink assignment. So the RB grouping size of CQIreporting could be a multiple of size of RB grouping in downlinkassignment. In one situation, the CQI reporting could be performedaccording to a unit of RBs smaller than the downlink assignment size oraccording to a unit consisting of a single RB. According to anothersituation, the reported CQI is applied according to the downlinkassignment by a unit of grouped RBs. As such, the CQI is generated andreported according to the unit of multiple RBs which could be used inthe actual downlink assignment.

DCI (Downlink Control Information)

The DCI provides the terminal (e.g., UE) with the necessary informationfor proper reception and decoding of the downlink data transmission.Information delivered in the DCI may include or indicate a DCI formatindicator, resource block assignment, modulation and coding scheme,redundancy version, new data indicator, Hybrid ARQ (HARQ) processnumber, precoding information, the number of the transmission layer,PUCCH transmit power control message and RNTI.

Since many transmission modes exist in LTE depending mostly on the MIMOmode (e.g., transmit diversity mode, spatial multiplexing mode), acorrespondingly high number of types (formats) of DCI are also needed.As such, a DCI format indicator is implemented as a DCI field.Scheduling in the time and frequency domains is delivered via a resourceblock assignment field. The modulation and coding scheme indicates thetype of modulation and error correction coding for scheduled transportblock. Sometimes, modulation and coding for a second codeword may betransmitted only when the two codewords are used in spatial multiplexingMIMO mode. HARQ-related information includes redundancy version, newdata indicator and HARQ process number. For MIMO support, precodinginformation and the number of the transmission layer may be included. Aspreviously noted, the acronym “RNTI” refers to a Radio Network TemporaryIdentifier. The RNTI is used to identify a UE when a Radio ResourceControl (RRC) connection exists. The following types of RNTI aredefined: C-RNTI (Cell RNTI), S-RNTI (Serving RNC RNTI) and U-RNTI (UTRANRNTI).

In order for future telecommunication systems to support increasinglyhigh data rates and a higher number of transmission antennas, additionalUE-specific RS is provided. Since the RS itself is considered asoverhead from a system perspective, the amount of the RS should bebalanced due to the tradeoff between the channel estimation performanceand the system throughput. According to embodiments of the presentinvention, if the RS is configured to be processed over several RBs(see, e.g., FIG. 14B), the channel estimation performance based on theRS is enhanced based on the system bandwidth.

According to particular embodiments, in estimating a channel (e.g., acondition of the channel), a UE bundles the received RBs into bundles ofone or more RBs, where the size of the RB bundle is dependent on thesystem bandwidth. According to one embodiment, the size of the systembandwidth is provided to the UE from the network.

The UE-specific RS allows the UE to estimate the downlink channelstatus. An aspect of the present invention draws a relationship betweenthe UE-specific RS and the downlink channel assignment which isscheduled by a NodeB. According to embodiments of the present invention,the manner in which RBs are bundled by a UE to perform channelestimation is associated with the grouping of RBs in the downlinkchannel assignment (see, e.g., Table 1).

For convenience of notation, the terms RB bundling of UE-specific RS, RBbundling and, simply, bundling are used interchangeably in thedescription below.

RB Bundling of the Same Size as RB Grouping

The ultimate goal of UE-specific RS is to help the UE to demodulate thescheduled data without error. According to embodiments of the presentinvention, since UE-specific RS is closely related to data actuallyassigned to the scheduled UE, a relationship is drawn between theUE-specific RS and the scheduled data. According to a particularembodiment, the size of an RB bundle of UE-specific RS is equal to thesize of the RB grouping in the downlink assignment. By matching thesetwo sizes, the RS may be fully utilized within the allocated RBs withoutany waste of processing in the decoding of the RS.

An example of such matching is now described with reference to FIGS. 15Aand 15B. According to this example, the size of the system bandwidth is27 RBs. Referring back to Table 1, this particular size corresponds togroupings of three contiguous RBs. With reference to FIGS. 15A and 15B,contiguous RBs 1510, 1520 and 1530 are grouped together as RB group 1570in the downlink allocation. Similarly, contiguous RBs 1540, 1550 and1560 are grouped together as RB group 1580 in the downlink allocation.As illustrated in FIGS. 15A and 15B, RBs scheduled for a particular userdo not necessarily need to be contiguous. For example, RB groups 1570and 1580 are not contiguous. As such, RB groups in a particularassignment may be scattered, as illustrated in FIGS. 15A and 15B.

With reference to FIG. 15A, a UE estimates the channel based on the RSs(e.g., UE-specific RS) of individual RBs. That is, the UE estimates thechannel based on the RBs of RB group 1570 in isolation with respect toone another. That is, the UE estimates the channel based on RB 1510 inisolation, RB 1520 in isolation, and RB 1530 in isolation. The UEestimates the channels based on the RBs of RB group 1580 in a similarmanner. It is understood that, although the channel estimation isperformed based on each RB in isolation, this approach does notnecessarily require the implementation of multiple channel estimators.Rather, the channel estimation per each RB may be performed sequentiallyby a single channel estimator in a timely manner.

In contrast, with reference to FIG. 15B, the UE estimates the channelbased on the RSs (e.g., UE-specific RS) of a bundle of RBs. The size ofthe bundle may be at least two RBs. As illustrated in FIG. 15B, the UEestimates the channel based on a bundle of three RBs (corresponding togroup 1570) including RBs 1510, 1520, 1530 concurrently (the UEconcurrently uses or processes a combination of the RS informationprovided in the RBs 1510, 1520 and 1530). Similarly, the UE estimatesthe channel based on a bundle of three RBs (corresponding to group 1580)including RBs 1540, 1550, 1560 concurrently. The size of the bundle isequal to the size of the RB grouping (i.e., 3 RBs). Because the size ofthe RB grouping is dependent on the system bandwidth (see, e.g., Table1), the size of the bundle is also dependent on the system bandwidth.

Since the channel estimator of FIG. 15B has, at a given time, access toa higher quantity of RS than the channel estimator of FIG. 15A, theformer has additional freedom of signal processing on the channelestimation.

As previously explained, in the example illustrated in FIGS. 15A and15B, the size of the system bandwidth was assumed to be 27 RBs. Inaccordance with Table 1, according to one embodiment, the size of eachbundle is 3 RBs when the system bandwidth is between 27 RBs and 63 RBs.Also in accordance with Table 1, according to one embodiment, the sizeof each bundle is 2 RBs when the system bandwidth is between 11 RBs and26 RBs. Also in accordance with Table 1, according to one embodiment,the size of each bundle is 1 RB when the system bandwidth is equal to orless than 10 RBs. According to a particular embodiment, the RBs in aparticular bundle are contiguous.

RB Bundling Size as a Multiple of RB Grouping Size

Even though the minimum unit of downlink channel allocation may berelatively small (e.g., 3 RBs), the actual channel assignment may beperformed based on a larger unit, e.g., a multiple of minimum groupsize. According to embodiments of the present invention, the size of theRB bundles is equal to a multiple (e.g., an integer multiple) of thesize of the RB grouping. For example, if the size of the RB grouping is3 RBs, then the size of the RB bundles may be equal to 6 RBs, 9 RBs,etc.

An example of such matching is now described with reference to FIGS. 16Aand 16B. According to this example, the size of the system bandwidth is27 RBs. Referring back to Table 1, this particular size corresponds togroupings of three contiguous RBs. With reference to FIGS. 16A and 16B,contiguous RBs 1610, 1620 and 1630 are grouped together as RB group 1670in the downlink allocation. Similarly, contiguous RBs 1640, 1650 and1660 are grouped together as RB group 1680 in the downlink allocation.

With reference to FIG. 16A, a UE estimates the channel based on the RSs(e.g., UE-specific RS) of individual RBs. That is, the UE estimates thechannel based on the RB bundles (respectively corresponding to groups1670, 1680) in isolation with respect to one another. That is, the UEestimates the channel based on the RB bundle corresponding to group 1670in isolation and on the RB bundle corresponding to group 1680 inisolation.

In contrast, with reference to FIG. 16B, the UE estimates the channelbased on multiple RB bundles. As illustrated in FIG. 16B, the UEestimates the channel based on the bundles noted in the above paragraphconcurrently (the UE concurrently uses or processes a combination of theRS information provided in the RB bundles).

Non-Contiguous RB Bundling

According to embodiments of the present invention, the downlinkallocation is performed in a discontinuous manner in order to achieve anincreased diversity gain in the frequency domain. In that case, theallocated RBs may be separated from each other by one or more RBs.According to embodiments of the present invention, RB bundling is alsoapplied to a situation involving allocation of non-contiguous RBs. Assuch, bundling provides the channel estimator with additional freedom ofprocessing to the channel estimator without harming the channelestimation performance.

The example illustrated in FIG. 17A is similar to the exampleillustrated in FIG. 15B. In FIG. 17A, the UE estimates the channel basedon the RSs (e.g., UE-specific RS) of a bundle of RBs. The size of thebundle may be at least two RBs. As illustrated in FIG. 17A, the UEestimates the channel based on a bundle of three contiguous RBsincluding RBs 1710, 1711, 1712 concurrently (the UE concurrently uses orprocesses a combination of the RS information provided in the contiguousRBs 1710, 1711, 1712).

With reference to FIG. 17B, according to one embodiment, the UEestimates the channel based on a bundle non-contiguous RBs. For example,as illustrated in FIG. 17B, the UE estimates the channel based on abundle of five non-contiguous RBs including RBs 1710, 1713, 1716, 1719,1722 concurrently (the UE concurrently uses or processes a combinationof the RS information provided in the non-contiguous RBs 1710, 1713,1716, 1719, 1722).

RB Bundling Boundary Aligned with the Boundary RB Assignment

When RBs are grouped together in the downlink and the RBs are bundled bya scheduled UE, one or more of the bundles may include UE-specific RSspecific to other UEs. Here, according to certain embodiments describedearlier, such information intended for other UEs may be considered bythe UE in performing channel estimation. This may occur when thescheduled UE is not aware of the signature (or other characteristic) ofthe other UEs such that the scheduled UE can not fully utilize the RSinformation specific to the other UEs. As such, embodiments of thepresent invention are directed to align the boundary of an RB bundlewith only a portion of the corresponding RB grouping when the groupingis not entirely allocated to the scheduled UE. By aligning the boundaryof the bundled RB with only such a portion (the portion of the RBgrouping corresponding to the scheduled UE), the UE-specific RS for thescheduled UE may be utilized without interference from UE-specific RS ofthe other UEs.

An example of such an alignment is now described with reference to FIGS.18A and 18B. According to this example, the size of the system bandwidthis 27 RBs. Referring back to Table 1, this particular size correspondsto groupings of three contiguous RBs. With reference to FIGS. 18A and18B, contiguous RBs 1810, 1820 and 1830 are grouped together as RB group1870 in the downlink allocation. Similarly, contiguous RBs 1840, 1850and 1860 are grouped together as RB group 1880 in the downlinkallocation.

With reference to FIG. 18A, the UE estimates the channel based on abundle of three RBs (corresponding to group 1870) including RBs 1810,1820, 1830 concurrently (the UE concurrently uses or processes acombination of the RS information provided in the RBs 1810, 1820 and1830). As illustrated in FIG. 18A, the group 1880 is also allocated tothe scheduled UE. Specifically, the RS content of the group 1880corresponding to RBs 1840, 1850 (see, e.g., portion 1881) is allocatedto the scheduled UE. However, the RS content of the group 1880corresponding to RB 1860 (see, e.g., portion 1882), which containsUE-specific RS for other UEs, is also allocated to the scheduled UE.

With reference to FIG. 18B, according to one embodiment of the presentinvention, the boundary of an RB bundle is aligned with a portion of thecorresponding RB grouping that contains RS content allocated to thescheduled UE. For example, as illustrated in FIG. 18B, the bundlecorresponding to group 1880 is aligned to end at the boundary dividingportions 1881 and 1882. As such, the bundle is considered as afractionally bundled RB. In more detail, the bundle includes theportions of the group 1880 corresponding to RBs 1840 and 1850. However,the bundle does not include the portion of the group corresponding to RB1860. As such, the UE-specific RS for the scheduled UE may be utilizedwithout interference from UE-specific RS of the other UEs.

DCI Format Indication

According to embodiments of the present invention, a DCI field isestablished to impart information related to the bundling conceptsdescribed herein. This DCI field may be part of control signalingrelated to the downlink assignment conveyed via DCI on PDCCH.

Various embodiments will be described with reference to the DCIstructures illustrated in FIGS. 19A, 19B, 19C and 19D. If the size ofthe RB bundles is assumed to be equal to the RB group size which is usedin downlink scheduling (see, e.g., FIG. 15B), then it may not benecessary to indicate the RB bundling size to the UE. As such, theexisting DCI structure may not be modified (see, e.g., FIG. 19A).

If a UE may be controlled to switch between implementing RB bundling(see, e.g., FIG. 15B) and not implementing RB bundling (see, e.g., FIG.15A), then the DCI structure may be modified to include an indicator1910 indicating whether RB bundling is to be switched on or off (see,e.g., FIG. 19B).

If the size of the RB bundles is assumed to be a multiple of the RBgroup size which is used in downlink scheduling (see, e.g., FIG. 16B),then it may be necessary to indicate the RB bundling size to the UE. Assuch, the existing DCI structure may be modified to include an indicator1920, 1930 indicating the size of the RB bundles (see, e.g., FIGS. 19Cand 19D). In the structure illustrated in FIG. 19C, the structure alsoincludes the indicator 1910 that was described with reference to FIG.19B. In the structure illustrated in FIG. 19D, the indicator 1910 isomitted. This structure is suitable when the UE is configured torecognize that a particular bundling size (e.g., 0) corresponds to aswitching off of the RB bundling.

If the size of RB bundling is fixed to be equal to the size of RB group(e.g., the sizes provided in Table 1), then the additional fieldsdescribed with reference to FIGS. 19B, 19C and 19D may not be necessary.According to one embodiment, even if the size of the RB bundles isvariable, if a predetermined one-to-one mapping between RB bundling sizeand the DCI format is implemented, then further indicators relating tothe RB bundling may not be necessary. Once the UE is informed of the DCIformat, it may also determine the RB bundling size (also whether RBbundling is to be turned on) based on the predetermined mapping betweenthe RB bundling size and the DCI format.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses andprocesses. The description of embodiments of the present invention isintended to be illustrative, and not to limit the scope of the claims.Many alternatives, modifications, and variations will be apparent tothose skilled in the art.

1. A method of sizing bundled resource blocks (RBs) having at least oneuser equipment (UE)-specific demodulation reference signal in anorthogonal frequency division multiplexing (OFDM) system, the methodcomprising: receiving configuration information related to at least oneUE-specific demodulation reference signal; receiving a plurality ofresource blocks (RBs) from a network, wherein the plurality of resourceblocks comprises the at least one UE-specific demodulation referencesignal, at least one cell-specific demodulation reference signal ordata, wherein a number of the plurality of RBs is dependent on a size ofa system bandwidth, the size of the system bandwidth corresponding toone of four size ranges; and processing at least one of the receivedplurality of RBs by bundling the plurality of RBs into RB bundles,wherein the size of each RB bundle is based on the one of the four sizeranges.
 2. The method of claim 1, wherein processing at least one of thereceived plurality of RBs comprises reporting at least a channel qualityindicator (CQI), a precoder matrix indicator (PMI), or a rank indicator(RI).
 3. The method of claim 1, wherein the size of each RB bundlecomprises at least two RBs.
 4. The method of claim 1, further comprisingsizing an RB group for a downlink resource allocation according to thesize of the system bandwidth, wherein each RB bundle is sized accordingto the size of the RB group.
 5. The method of claim 3, wherein the sizeof each RB bundle is the same as the size of the RB group.
 6. The methodof claim 3, wherein the size of each RB bundle is a multiple of the sizeof the RB group.
 7. The method of claim 1, further comprising receivingthe size of a system bandwidth from a network.
 8. The method of claim 1,wherein the size of each RB bundle is 1 RB when the system bandwidth isless than 10 RBs.
 9. The method of claim 1, wherein the size of each RBbundle is 2 RBs when the system bandwidth is between 11 RBs and 26 RBs.10. The method of claim 1, wherein the size of each RB bundle is 3 RBswhen the system bandwidth is between 27 RBs and 63 RBs.
 11. The methodof claim 1, wherein each RB bundle comprises a plurality of contiguousRBs of the system bandwidth.
 12. A method of sizing bundled resourceblocks (RBs) having at least one user equipment (UE)-specificdemodulation reference signal in an orthogonal frequency divisionmultiplexing (OFDM) system, the method comprising: transmittingconfiguration information related to at least one UE-specificdemodulation reference signal; transmitting a plurality of resourceblocks (RBs) to a user equipment (UE), wherein the plurality of resourceblocks comprises the at least one UE-specific demodulation referencesignal, at least one cell-specific demodulation reference signal ordata, wherein a number of the plurality of RBs is dependent on a size ofa system bandwidth, the size of the system bandwidth corresponding toone of four size ranges; and receiving channel condition informationfrom the UE, wherein the channel condition information is determined byprocessing at least one of the received plurality of RBs by bundling theplurality of RBs into RB bundles, wherein the size of each RB bundle isbased on the one of the four size ranges.
 13. A user equipment (UE)sizing bundled resource blocks (RBs) having at least one user equipment(UE)-specific demodulation reference signal in an orthogonal frequencydivision multiplexing (OFDM) system, the UE comprising: an RF unit forreceiving configuration information related to at least one UE-specificdemodulation reference signal and receiving a plurality of resourceblocks (RBs) from a network, wherein the plurality of resource blockscomprises the at least one UE-specific demodulation reference signal, atleast one cell-specific demodulation reference signal or data, wherein anumber of the plurality of RBs is dependent on a size of a systembandwidth, the size of the system bandwidth corresponding to one of foursize ranges; and a processor for processing at least one of the receivedplurality of RBs by bundling the plurality of RBs into RB bundles,wherein the size of each RB bundle is based on the one of the four sizeranges.
 14. The UE of claim 12, wherein the size of each RB bundlecomprises at least two RBs.
 15. The UE of claim 12, wherein theprocessor sizes an RB group for a downlink resource allocation accordingto the size of the system bandwidth, wherein each RB bundle is sizedaccording to the size of the RB group.
 16. The UE of claim 14, whereinthe size of each RB bundle is the same as the size of the RB group. 17.The UE of claim 14, wherein the size of each RB bundle is a multiple ofthe size of the RB group.
 18. The UE of claim 12, wherein the RF unitreceives the size of a system bandwidth from a network.
 19. The UE ofclaim 12, wherein the size of each RB bundle is 1 RB when the systembandwidth is less than 10 RBs.
 20. The UE of claim 12, wherein the sizeof each RB bundle is 2 RBs when the system bandwidth is between 11 RBsand 26 RBs.
 21. The UE of claim 12, wherein the size of each RB bundleis 3 RBs when the system bandwidth is between 27 RBs and 63 RBs.
 22. TheUE of claim 12, wherein each RB bundle comprises a plurality ofcontiguous RBs of the system bandwidth.